Using Unidirectional Rotations to Improve Vestibular System Asymmetry in Patients with Vestibular Dysfunction

Summary

A new rehabilitation method is presented for rebalancing the vestibular system in patients with asymmetric responses, which consists of unidirectional rotations toward the weaker side. By directly modifying the vestibular pathway rather than enhancing the multisensory aspects of compensation, asymmetry can be normalized within 1-2 sessions and show lasting effects.

Abstract

The vestibular system provides information about head movement and mediates reflexes that contribute to balance control and gaze stabilization during daily activities. Vestibular sensors are located in the inner ear on both sides of the head and project to the vestibular nuclei in the brainstem. Vestibular dysfunction is often due to an asymmetry between input from the two sides. This results in asymmetrical neural inputs from the two ears, which can produce an illusion of rotation, manifested as vertigo. The vestibular system has an impressive capacity for compensation, which serves to rebalance how asymmetrical information from the sensory end organs on both sides is processed at the central level. To promote compensation, various rehabilitation programs are used in the clinic; however, they primarily use exercises that improve multisensory integration. Recently, visual-vestibular training has also been used to improve the vestibulo-ocular reflex (VOR) in animals with compensated unilateral lesions. Here, a new method is introduced for rebalancing the vestibular activity on both sides in human subjects. This method consists of five unidirectional rotations in the dark (peak velocity of 320°/s) toward the weaker side. The efficacy of this method was shown in a sequential, double-blinded clinical trial in 16 patients with VOR asymmetry (measured by the directional preponderance in response to sinusoidal rotations). In most cases, VOR asymmetry decreased after a single session, reached normal values within the first two sessions in one week, and the effects lasted up to 6 weeks. The rebalancing effect is due to both an increase in VOR response from the weaker side and a decrease in response from the stronger side. The findings suggest that unidirectional rotation can be used as a supervised rehabilitation method to reduce VOR asymmetry in patients with longstanding vestibular dysfunction.

Introduction

Vestibular dysfunction is a common disorder with a prevalence of ~35% in adults above 40 years old¹. Most vestibular disorders result in an asymmetry between input from both sides, resulting in an illusion of rotation called vertigo. In the absence of normal vestibular function, even simple daily activities can be challenging. Vestibular dysfunction is often quantified by the vestibulo-ocular reflex (VOR). During natural activities, such as walking or running, the VOR moves the eyes in the opposite direction and with the same velocity as head movement. This reflex has a short latency of ~5 ms, and it is mediated in the horizontal plane thr....

Protocol

The data presented here and previously published³ were obtained by studies carried out in accordance with the recommendations of the Ethics Committee of Shahid Beheshti University of Medical Sciences, Tehran, Iran and a protocol that was approved by the Institutional Review Board of the University.

1. Participant screening and preparation

1. Recruit participants who have had a history of balance problems for more than one year.
   NOTE: Vestibular compensation happens most effectively over the first month after a lesion. The one year timepoint was chosen to provide enough time for natural compensation to r....

Results

Short-term effects of the unidirectional rotation were evaluated by measuring the VOR with a 0.2 Hz (40°/s) sinusoidal rotation test at 70 min after rehabilitation³. Figure 2 shows the peak eye velocities during the VOR responses to rotations in the two directions (Figure 2A) and the change in the DP (Figure 2B). Following unidirectional rotation, the response to rotations in .......

Discussion

The rehabilitation method presented here consists of repeated unidirectional rotations in the dark toward the less responsive (LR) side in patients with vestibular imbalance and VOR asymmetry. Most rehabilitation techniques enhance multisensory integration in order to improve balance^{16,17,18,19,20}. The method presented here targets the vestibular pathway, and .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
VEST operating and analysis software	NeuroKinetics
Electronystagmograph	Nicolet	Spirit Model 1992	Equipment used for collecting the data presented in the Results section
I-Portal NOTC (Neurotologic Test Center)	NeuroKinetics		Equipment shown for current studies and shown in the movie